In hemodialysis treatment, a conventional hemodialysis apparatus includes a blood circuit to extracorporeally circulate blood of a patient, a dialyzer provided at the blood circuit, a peristaltic blood pump, and a dialysis device. The dialysis device allows dialysate to flow in and out to the dialyzer from the dialysis device to perform hemodialysis and ultrafiltration. The blood circuit is provided with an arterial blood circuit having an arterial needle at an end thereof and a venous blood circuit having a venous needle at an end thereof.
When the arterial needle and the venous needle are inserted to the patient, and the blood pump is turned on, blood of the patient flows through the arterial needle into the arterial blood circuit, the dialyzer, and the venous blood circuit in sequence, and then flows back into the body of the patient through the venous needle. The dialyzer includes hollow fibers forming membranes for hemodialysis. The blood flows inside of the hollow fibers. The dialysate, which has a predetermined concentration and is supplied from the dialysis device, flows outside the hollow fibers (i.e., between outside surfaces of the hollow fibers and an inside surface of a case of the dialysis device). Waste products in the blood flowing in the inside of the hollow fibers permeate into the dialysate through the membranes.
The blood flows back to the body of the patient after flowing through the venous blood circuit and after the waste products being removed from the blood. Also, the dialysis device is provided with an ultrafiltration pump that removes water from the blood. The blood is also ultrafiltrated through the membranes during the hemodialysis treatment. A volume of water to be ultrafiltrated by the ultrafiltration pump (i.e., an ultrafiltration rate) is adjusted by controlling a driving rate of the ultrafiltration pump.
However, if the volume of water to be ultrafiltrated (the ultrafiltration volume) is large, it is necessary to increase the ultrafiltration rate, and the patient may develop shock syndromes such as hypotension depending on the health condition of the patient. To detect the predictor of such shock syndromes, a device has been proposed to measure a hematocrit value (red blood cell volume ratio in blood) and monitor the patient by calculating a variation rate of a circulating blood volume (ΔBV) from the hematocrit value.
Normally, the variation rate of the circulating blood volume (ΔBV) becomes lower with the time course of treatment, but when drastic drop of ΔBV occurs, it is regarded as the predictor of shock syndromes such as hypotension. However, it is possible to prevent shock syndromes to occur by applying some treatments (fluid replacement, terminating hemodialysis, and the like) at the time of the drastic drop of ΔBV. Thus, an apparatus for hemodialysis is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2004-977811 that measures hematocrit values of a patient sequentially and calculates the variation rate of the circulating blood volume (ΔBV) of the patient from these hematocrit values.
An ultrafiltration volume controlled by the ultrafiltration pump described above is to be set so as to make a body weight of the patient close to a dry-weight of the patient (body weight of the patient when a volume of an interstitial fluid outside of cells is properly adjusted). The dry-weight of the patient is estimated based on experiences of a medical staff, such as a medical doctor (the dry weight obtained in such a way is called “the estimated dry weight”), and the ultrafiltration volume is to be set so as to be the estimated dry weight. The nearness of the estimated dry weight to the true dry weight (called dry weight) can be grasped by whether PWI (Plasma Water Index), which is obtained by a formula dividing a variation rate of a circulating blood plasma volume (ΔCPV %) by a variation rate of body weight (ΔBW %), is within a predetermined range.
However, the conventional hemodialysis apparatus as described above has the following problems.
Although the conventional hemodialysis apparatus as described above can evaluate whether the hemodialysis treatment has been appropriate with the estimated dry weight approximating to the dry weight based on PWI, the appropriateness of the treatment can only be evaluated after the treatment is completed because the proper value of PWI may vary over time or depending on the dialysis condition. Thus, it can not be evaluated whether the hemodialysis treatment is proceeding properly with the estimated dry weight approximating to the dry weight.
On the other hand, it has been known in a stable patient undergoing hemodialysis treatment for relatively long term that time series data (especially standardized data) are reproducible when they are obtained by measuring parameters such as the variation rate of the circulating blood volume, ΔBV, which relate to the concentration of blood circulating extracorporeally, in time series at a plurality of points during hemodialysis treatment process. Thus, the present applicants investigated a hemodialysis apparatus which can grasp the appropriateness of hemodialysis treatment during the course of treatment in real time by taking advantage of the reproducibility of time series data.
The present invention is achieved by taking this situation into consideration and provides an apparatus and method for hemodialysis by which a plurality of the courses (time series data) for appropriate hemodialysis treatments are stored where the estimated dry weight approximates to the dry weight, and in which, in the hemodialysis treatments thereafter, it is easy to evaluate whether the hemodialysis treatment is following the course in which the treatment would produce an appropriate result approaching the dry weight.